Improving the cut growth resistance of butadiene-vinyl pyridine rubbery copolymers



Patented Oct. 9, 1951 'nvrraovme THE om GROWTH RESIST,- AN'CE or gBUTA'DIENE-YINYL rmmmn 'RUBBERY GOPOL'YMERS Bernard 0. Barton, Clifton, N. ,J., aassignor to United States Rubber Company, .New York, N. Y., a corporation ofNewJel'sey No Drawing. Application April 1, 1948,

I Serial No. 13,496

.10 Claims. (01. J260--.-.31..8)

I have 'now found that the out growth resist- 7 time of butadiene-vinyl pyridine rubbery copoly- :mers can :be greatly enhanced by adding there- :to, prior tmcuring, .azsmall amount of an aromatic carboxylic .acid. In some cases as :little as 0.1 :part by weight of the aromatic carboxylic :acid

;per 100 parts by weight of butadiene-vinyl pyri- .zdine copolymer issuflicient toshow improvement. However I prefer to employ "from 1 to 6 parts by weight of the aromatic carboxylic acid per 100 parts by weight of the butadiene-vinyl pyridine rdbbery copolymer because maximum -improyement in-cut growth-resistance is ifound :within this range. Larger amounts than -6% may be used but are generally unnecessary.

In a typicalmethod of practicing my invention,

a vulcanizable mix is prepared containing the butadiene-vinyl pyridine rubbery copolymer and "the .usual rubber compounding components such as carbon black, zinc oxide, softeners such aspine tar or asphalt or thelike, stearic acid, the cus- 'tomary 'vulcanizing agent, generally sulfur, and vulcanization accelerators. In the formulation ofthe compound, in accordance with my inven- "tionthereisincorporated a small amount of the aromatic carboxylic acid. The compounding is 'usually-effected-onthe regular rubber mill in the usual manner. 'Theresulting compound is then shaped in the usual way and vulcanized in accordancewith conventional practice. 'The resulting 'vu'lcan'izate exhibits greatly increased cut igrowth resistance over the same material made without the aromatic ;carboxylic --acid, and none of its .other physical properties are impaired. 'Ehe practice .of -my invention does .not interfere in any .respect with the conventional compounding and .vulcanizing techniques.

Any aromatic carboxylic -:acid may ebezemployed .i'in the practice .of .my invention. Examples of :such acids which.may .be very successfully emyployed .areSalicylic .acid, benzoic ,acid, .phthalic azcid-.-pr.more usually;phthalicranhydride (italoeing ainderstood thattheanhydrides of the aromatic molycarboxylic acids .are usedequiva-lently -.wit:h .theacids themselves in practicing the present in- Mention), penitrobenzoic acid, alpha-naphthoic acid, vbeta-naphthoic acid, naphthalic acid or anhydride, gallic acid, etc. Any other aromatic carboxylic acid may be employed. I generally use the monocyclic and bicyclic aromatic carboxylic acids since they are most readily available. The aromatic carboxylic acid employed is generally free from substitution on the ring with groups other than hydroxyl 0r nitro groups. However they may be ring-substituted with groups such as halogensuch as chlorine, amino groups, alkyl groups (as in toluic acid and xylic acid), a phenyl .group (as in diphenic acid), where such other groups do not cause the resultingpompound to exert a harmful effect upon the butadiene-vinyl pyridine rubbery copolymer. The aromatic :carbcxylicacid is usually a monocarboxylic acid but it may be a dicarboxylic acid or even @a .tricarboxylic acid.

The preferred aromatic carboxylic acids for -use inthe practiceof my invention are the monocyclic :and ibicyclic monocarboxylic rand dicar- 'boxylic acids, and :anhydrides pf such dicarboxylic "acids, said acids either being otherwise "unsubstituted on the :ring or being ring-substituted with nitro or hydroxyl groups. Benzoic acid, salicylic :acid and phthalic anhydride are :most highly preferrediorusein my invention because they combine low :cost with high effectiveness :in improving cut growth resistance.

I have :found {that ordinary aliphatic saturated monocarboxylic and ,polycarboxylic acids, such as the unsubstituted fatty acids and aliphatic dibasic acids, are not capable of producing the marked increase in out growth resistance of butadiene-vinyl pyridine rubber that is produced by the aromatic carboxylic acids of my invention. This is illustrated below by'a comparison of Ex an' ples9 to 11 'with'comparative Examples =5 to 3 whereinacidsof the present invention were used.

Instead of the aromatic carboxylic acids specifically named above, 'I may employ halogensubstituted aromaticcarboxylic acids such as the chlorobenzoic acids, amino-substituted aromatic carboxylic acids such as the zamlnobenzoicacids, other hydroxy substituted aromatic carboxylic acids such as m-hydroxybenzoic acid, p-hydroxybenzoic acid, etc., protocatechuic acid, isophthalic acid. er ph halic acid, nitronanhtalic acids, etc.

,Any butadiene-vinyl pyridine rubbery copolymer may be used in the practice of the present invention. I usually employ :a rubbery .copoly gmer of butadiene and 2-vinyl pyridine but the vinyl group may be in any other position on the pyridine, as exemplified by 4-vinyl pyridine. The vinyl pyridine may also be substituted on the pyridine with an alkyl group, as typified by 2- Stock 2A The same as stock 2, but containing in addition 2.0 parts of salicyclic acid.

methyl-S-vinyl pyridine. The proportions of 5 EXAMPLE 3 butadiene-L3 and the vinyl pyridine used in mak- St k 3 ing the rubbery copolymer may vary widely as is 06 well known in the art. Usually from 25 130 75% Butadiene-vinylpyridine copolymer 100 of butadiene and correspondingly from. '75 to 25% Carbon black 50 of the vinyl pyridine are employed. The. poly- 10 Asphalt 7 merization of these two monomers is conducted Benzylidenebis-dimethyldith in any manner known to the art, aqueous emularbamate 1 sion polymerization generally being used. The :z xid 1 method of making the butadiene-vinyl pyridine Sulphur 1.5 rubbery copolymer does not constitute per se an Stock 3A part of the present invention.

The following experiments show the efiective- The same as Stock 3, but containing in addiness of aromatic carboxylic acids in improving tion 2.0 parts of salicyclic acid. out growth resistance of rubbery butadiene-vinyl The foregoing stocks were compounded on a pyridine copolymers. Contrary to the wellrubber mill in the ordinary manner. Test reknown retarding effect which acids exert on the sults on these stocks, after curing in a mold in curing of natural rubber and GR-S (butadienea press under 45 pounds per square inch steam styrene rubbery copolymer) the effect which the pressure for various times, were as follows:

Out

M dul Time of g ggg st ress i z Tensile Per Cent Jure kilo 0195 300 Strength Elong. at (minutes) Elong (p. s. 1.) Break perinch oi s i) p growth) V 450 1, 300 2, 700 500 Stock 1 (no acid) 50 370 1, 450 2. 700 450 120 305 1, 000 2,500 450 so 895 1, 100 2, 400 550 Stock 1A (2.0 pts. salicylic acid) 60 1, 000 1, 200 2. 600 510 120 910 1, 400 2,500 490 25 290 590 1, 250 590 Stock 2 (no acid) 45 280 900 2, 000 500 90 100 1, 000 2, 150 510 25 .520 375 1, 100 725 Stock 2A (2.0 pts. salicylic acid) 45 485 575 l, 775 6 90 520 890 2,250 555 25 250 1, 160 2, 275 515 Stock 3 (no acid) 45 220 1, 375 2, 400 470 00 190 1, 275 2. 000 515 25 690 1, 050 2, 725 600 Stock 3A (2.0 pts. salicylic acid) 45 500 1,170 2. 710 580 90 040 1,480 2,210 40o aromatic carboxylic acids employed in accord- From the foregoing table, the greatly superior ance with the present invention exerts upon the out growth resistance of the vulcanizates from, curing of the vinyl pyridine rubber is either nil mixtures containing salicyclic acid over those or small as judged by the modulus of the vulcontaining no acid is readily apparent. canizate- EXAMPLES 4 TO 11 The copolymer used in all of the experiments T f t h described hereinafter was made from monomers 5O he ouowlpg are add1t19na.1exp.enmen consisting of butadiene-l,3 and 2-vinyl pyridine mg thepffectlvengss ofsahcyhf p f in a ratio of '75 parts butadiene to 25 parts 2-vinyl P f anhydnde P'mtrobenzmc 1 m pyridine An parts herein are by Weight improving out growth life in accordance Wlth, my

invention. Comparisons are made with vulcaniz- EXAMPLE 1 ates which were identical except that they con- ,S'tock 1 tained aliphatic saturated carboxylic acid, namely Part by weight acetic acid (Example 9), oxalic acid (Example Butadiene-vinylpyridine copolymer 100 10) and stearic acid (Example 11). All of the Carbon black 50 stocks tested except the ones used in the first inc Oxide 5 two runs (Example 4) contained acid in the ine tar 5 amount indicated added to a portion of the fol- Stearic acid 3 ,lowing master batch prepared with the same co- Benzothiazyldisulfide 0.15 polymer as was used in the previous examples. sulphur Parts by weight Stock 111 Butadiene-vinylpyridine copolymer 100 The same as Stock 1, but containing in addition f black 50 2.0 parts of salicyclic acid. g l g 1110 OX1 e EXAMPLE 2 Sulfur 2 Stock 2 Benzylidene bis-dimethyldithio- Butadiene-vinylpyridine copolymer 100 carbamate Carbon black 5o The stress of 300% elongation and the cut Asphalt '7 growth resistance were determined on portions of Ben othiazyldisulfide 3 stock containing the various acids, cured for 30 p r 1.5 minute and 0 minutes at 4.5 p. s. i. steam presawdeee sure as indicated. As a-=contro1, the'same tests were-made on a portion of thepured master batch econ ainin noaddedacid.

6 'diene-vinyl pyridine rubbery copolymer the' 'cut growth resistance of which is sub'stan-tially en- "han'ced by curing in the presence 'Oflfl llldillifil Partsiby; 1 *Modulus CutGrowth Wt. ofAcid C ure(M1n- Stress at Resistance Example ggggg g g? utes at 300% (-kllQCyCleS glaster 45# steam) Elongation '})el"111(i]]11 bath) I a (ps. 1.) 0 grow fGOZ 1,730 60 '30 1,450 220 60 1, 675 275 "2 30 1,700 290 2.8, 360, 1,810 1265 3:2 30 1,350 170 3.i2j 130; -1,750 265 3. 6 30 1, 550 290 3. 6 60 1, 725 270 1.3 30 1,950 60 1. 3 60 2, 150 70 2.8 30 1,875 135 2. 8 60 2, 100 80 6.4 30 1,450 125 6.4 60 1,600v 130 EXAMPLES 12 o Oon- Acids trol Example N o 12 13 14 Master Batch--. 159. 5 159. 5 159. 5 159. 5

Acid 3 Stress At 300% Elongation (p. s. i) l, 800 l, 825 1, 610 960 Out Growth Resistance (kilocycles per inch of growth) 40 185 70 130 The variations in stress and in tensile strength of the various materials made as described in the foregoing examples are without any substantial significance. All of the stocks tested were good stocks.

From the foregoing it will be'apparent that'the present invention provides a simple and economical method of overcoming the serious disadvantage of vulcanizates made from rubbery butadiene-vinyl pyridine copolymers, namely their low resistance to out growth. Incorporation of the aromatic carboxylic acids of the present invention into the mix is carried out readily by standard technique and standard compounding and vulcanizing equipment are employed. The aromatic carboxylic acids do not have any adverse or deleterious effect during compounding and vulcanizing or upon the vulcanized product. The preferred aromatic carboxylic acids namely phthalic anhydride, salicylic acid and benzoic acid, arranged in order of increasing cost at the present-day market, are comparatively cheap and readily available and therefore do not present any problem of unduly increasing the cost of manufacture of cured butadiene-vinyl pyridine copolymer rubber products.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. As a new composition of matter, cured butaselected from the group consisting of ring-carboxylic aromatic monocarboxylic and polycarboxylic acids and. anhydrides of such polycarboxylic acids, in an amount ranging from 0.1 to 6% by weight based on the weight of said rubbery copolymer.

2. As a new composition of matter, cured butadiene-vinyl pyridine rubbery copolymer the out growth resistance of which is substantially enhanced by curing in the presence of a material selected from the group consisting of ring-carboxylic aromatic monocarboxylic and polycarboxylic acids and. anhydrides of such polycarboxylic acids, in an amount ranging from 1 to 6% by weight based on the weight of said copolymer.

3. As a new composition of matter, cured butadiene-vinyl pyridine rubbery copolymer the out growth resistance of which is substantially enhanced by curing in the presence of from 1 to 6% by weight based on the weight of said copolymer of salicylic acid.

4. As a new composition of matter, cured butadiene-vinyl pyridine rubbery copolymer the out growth resistance of which is substantially enhanced by curing in the presence of from 1 to 6% by weight based on the weight of said copolymer 7 of benzoic acid.

5. As a new composition of matter, cured butadiene-vinyl pyridine rubbery copolymer the out growth resistance of which is substantially enhanced by curing in the presence of from 1 to 6% by weight based on the weight of said copolymer of phthalic anhydride.

6. As a new composition of matter, a vulcanizable mixture containing a butadiene-vinyl pyridine rubbery copolymer and from 1 to 6% by weight based on the weight of said copolymer of a material selected from the group consisting of ring-carboxylic aromatic monocarboxylic and polycarboxylic acids and anhydrides of such polycarboxylic acids, said mixture upon vulcanization yielding a vulcanized rubber having a out growth resistance which is substantially greater than an identical rubber which does not contain said material.

'7. The process of making vulcanized butadiene-vinyl pyridine copolymer rubber of substantially increased cut growth resistance which comprises forming a vulcanizable mixture containing butadiene-vinyl pyridine rubbery copolymer and from 1 to 6% by weight based on the weight of said copolymer of a material selected from the group consisting of ring-carboxylic aromatic monocarboxylic and polycarboxylic acids and anhydrides of such polycarboxylic acids, and vulcanizing said mixture.

Number 8. The process of claim '7 wherein said acid is 2,331,059 salicylic acid. 2,396,967 9. The process of claim 7 wherein said acid is 5 2,402,020 benzoic acid.

10. The process of claim '7 wherein said acid is phthalic anhydride. Number 117,438 BERNARD C. BARTON. 10 238,2 7 413,283

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Jones -1. Aug. '7, 1945 Phillips Mar. 19, 1946 Cislake June 11, 1946 FOREIGN PATENTS Country Date Australia Sept. 9, 1943 Switzerland Oct. 16, 1945 Great Britain July 11, 1934 OTHER REFERENCES The Vanderbilt 194s Rubber Handbook, pp. 436 15 to 439, Vanderbilt 00., 1948. 

1. AS A NEW COMPOSITION OF MATTER, CURED BUTADIENE-VINYL PYRIDINE RUBBERY COPOLYMER THE CUT GROWTH RESISTANCE OF WHICH IS SUBSTANTIALLY ENHANCED BY CURING IN THE PRESENCE OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF RING-CARBOXYLIC AROMATIC MONCARBOXYLIC AND POLYCARBOXYLIC ACIDS AND ANHYDRIDES OF SUCH POLYCARBOXYLIC ACIDS, IN AN AMOUNT RANGING FROM 0.1 TO 6% BY WEIGHT BASED ON THE WEIGHT OF SAID RUBBERY COPOLYMER. 